Chapter 7: Bone Tissue

functions of the skeleton

• support

• protection

• movement

• electrolyte balance

• acid-base balance

• blood formation

• hormone secretion

osseous tissue

connective tissue in which the matrix is hardened by the deposition of calcium phosphate and other minerals

mineralization (calcification)

hardening process

what makes up the bone

osseous tissue, blood, bone marrow, cartilage, adipose tissue, nervous tissue, fibers

what kind of bones do cranial bones form? where else do these kind of bones form

flat bones (thin curved plats)

• sternum (breast)

• scapula (shoulder blades)

• ribs

• hips

what are the most important bones in movement? where can you find them

long bones that serve as a lever

• limbs

• digit bones

short bone and irregular bones. where can you find them

bones that don’t fit the long or flat bone groups

• wrist, ankle (short)

• vertebrae, some skull bones (irregular)

compact, dense, cortical bone

outer shell of dense white osseous tissue that encloses the marrow cavity

marrow (medullary cavity)

contains bone marrow

spongy bone

ends of bone where the central spacy is occupied by a more loosely organized form of osseous tissue

what is the ratio of compact bone to spongy bone

¾ : ¼

principle features of long bone

diaphysis and epiphysis

diaphysis

provides leverage

epiphysis

enlarged to strengthen the joint and provide added surface area for the attachment of tendons and ligaments

what is unique about mature bone

exhibits epiphyseal line of slightly dense spongy bone between the epiphysis and diaphysis (remnant of a childhood growth zone aka epiphyseal plate)

articular cartilage

a hyalin cartilage that covers the joint surface where one bone meets another

articular cartilage along what what enables a joint to move easily

lubricating fluid

nutrient foramina

minute holes in the blood where blood vessels can penetrate

periosteum

sheath that covers the bone that provides strong attachment and continuity from muscle to tendon to bone

what is the periosteum made of

outer fibrous layer, inner osteogenic layer

What are 2 pathways of the outer fibrous layer

• collagen fibers penetrate into the bone matrix as perforating fibers

• continuous with the tendons that bind muscle to bone

endosteum

thin layer of reticular connective tissue that lines the internal marrow cavity, covers surfaces of spongy bone, and lines a canal system in compact bone

function of flat bone

shield like plates that protect delicate organs (brain and heart), and form broad surfaces for muscle attachment (scapula, hip)

2 layers of flat bone

inner and outer tables (sandwiching spongy bone)

diploe definition and function

spongy layer in the cranium

absorb the impact

what does the epiphyseal line mark

site of epiphyseal plate that has ossified (closed). once closed, growth in length no longer occurs at the site

4 types of bone cells

• osteogenic

• osteoblasts

• osteoblasts

• osteoclasts

osteogenic cells

stem cells that give rise to other bone types from mesenchyme

where do you find osteogenic cells

endosteum, inner layer of periosteum, central canals

what is unique about osteogenic cells

only cells capable of dividing continually and producing more bone cells

what do osteogenic cells become

osteoblasts

osteoblasts

bone forming cells that synthesize the organic matter of the bone to promote mineralization (formation of the organic bone matrix)

osteogenesis

bone-building activity

what do osteoblasts from

rows in the endosteum and inner layer of the periosteum

what tissue do osteoblasts resemble

cuboidal epithelium on the bone surface

What do osteoblasts consist of

mitochondria, rough ER, and secretory vessicles

What stimulates the acceleration of osteogenic mitosis

stress and fractures

osteocyte

former osteoblasts that are embedded in the matrix

what % of bone cells do osteocytes make up? how long do they live?

90-95%, decades

where do osteocytes live and define that

lacunae (cavities in a bone)

canaliculi

slender channels that interconnect lacunae

describe the dendrite process for osteocytes

cytoplasmic processes that reach into the canaliculi to contact the processes from neighboring osteocytes, blood vessels, other osterblasts

how do osteocytes pass nutrients and how do they dispose of waste

gap junctions where their processes meet to pass nutrients and signals

pass their metabolic wastes to blood vessels

what is unique about osteocytes

• resorb or deposit bone matrix that contributes to homeostasis of bone density and blood concentrations

• strain sensors

why are osteoblasts and osteocytes important for endocrine cells

a hormone secretes osteocalcin that’s responsible for fight-or-flight

osteocalcin

• inhibits the parasympathetic nervous system and allows the sympathetic system to work unopposed

• stimulates the pancreas to make insulin

• increase the insulin sensitivity of fat cells

• acts on skeletal muscles to promote energy availability and capacity for exercise

• influence brain dev and function and male fertility

osteoclasts

bone dissolving cells on the bone surface

osteolysis

osteoclasts dissolves bone

where do osteoclasts develop

bone marrow stem cells as blood cells (independent of blast, clast, and cytes)

What is the reason behind the large size of osteoclasts

several stem cells fuse together to form osteoclast (150 micrometer and 3-4 nuclei)

ruffled border

side of osteoclast facing the bone surface with many deep infoldings of the plasma membrane that increase surface area and efficiency of bone resorption

resorption bays

etched pits in the bone where osteoclast reside

what cells perform osteogenesis? what bone cell performs osteolysis

• osteocytes and osteoblasts

• osteoclast

lacunae

Spaces between lamellae that contain osteocytes

matrix (bone)

stony matter that surrounds the osteocytes and lacunae

what percent of the matrix is organic? what is it synthesized by? what are these organic substances

• 1/3 organic

• osteoclasts

• collagen, protein-carb complexes

what makes up the majority of the inorganic matter in the matrix

85% hydroxyapatite (crystallized calcium phosphate)

compact bone contains

• concentric lamellae

• central (haversian) canal

• osteon (haversian system)perforating canals

concentric lamellae

onion like layers of matrix arranged around the central canal

osteon (haversian system)

• basic structural unit of compact bone

• cylinder of tissue surrounding a central call

• made up of central canal and its lamellae

perforating canals

connects central canals of 2 neighboring osteons

what are central and perforating canals lined with

endosteum

what separates each osteon

cement line that blocks microfractures from spreading

how do the central canals get fed and dispose of waste

foramina open into the perforating canals that cross the matrix

• waste is removed by the blood stream

circumferential lamellae

inner and outer boundaries of dense bone hat run parallel to the bone surface

interstitial lamellae

irregular regions, remains of old osteons that broke down

spongy bone consists of

spicules (rods or spines) and trabeculae (thin plates or beams)

bone marrow

soft tissue that occupy the marrow cavity

red bone marrow (myeloid tissue)

hematopoietic tissue (tissue that produce blood cells) that fills the marrow cavity

yellow bone marrow

fatty bone marrow that replaces red marrow in adults

where is red marrow limited to in adults

skull, vertebrae, ribs, sternum, hip, and proximal heads of the humerus and femur

Does yellow marrow produce blood

no, but if needed it can turn back into red marrow

ossification (osteogenesis)

bone formation

2 method of ossification

intramembranous and endochondral

intramembranous ossification

produces flat bones of the skull, clavicle, and part of the mandible

what are the 4 steps to intramembranous ossification

1. mesenchyme (soft tissue w/ blood vessels) condenses. mesenchymal cells —> osteoblasts and secrete osteoid tissue (prebone)

2. osteoblasts deposit minerals on osteoid, hardening it. osteoblasts —> osteocytes

3. periosteum and trabeculae forms

4. osteoblasts deposit bone on surfaces, creating thick compact bone

endochondral ossification

bone develops from preexisting model composed of hyalin cartilage

when does endochondral ossification begin

sixth week of fetal development

6 steps of endochondral ossification

1. cartilage model: hyaline cartilage covered with fibrous perichondrium forms

2. primary ossification center: walls calcify, osteoblasts forms a bone collar around the cartilage

3. marrow cavity formation: cells digest the cartilage and osteoblasts deposit bone layers

4. secondary ossification centers: epiphyses, forms secondary ossification centers and marrow cavities

5. epiphyseal plate: cartilage remains at the ends a articular cartilage and in the epiphyseal plate

6. adult bone: epiphyseal plate disappears, marrow cavities join to make adult bone

metaphysis

where epiphysis and diaphysis meets

trabeculae

thin plates of bone found in spongy bone

zone of reserve cartilage

furthest from the marrow cavity

consists of: hyalin cartilage w/ resting chondrocytes

zone of cell proliferation

chondrocytes multiply and arrange themselves into columns of lacunae

• accounts for child growth in height

zone of cell hypertrophy

mitosis stops, cells begin hypertrophy (enlarge), walls of the matrix between the lacunae become thin

• accounts for child growth in height

zone of calcification

minerals are deposited in the matrix between the columns of lacunae and calcify cartilage for temporary support

zone of bone deposition

walls between the lacunae break down and chondrocytes die, forming channels. blood vessels invade those channels, osteoblasts create bone layers, and osteoclasts dissolve cartilage, resulting in spongy bone

epiphyseal line

slightly denser spongy bone

appositional growth (in mature bones only!!!)

the deposition of new tissue at the surface (widening of the bone) that occurs by intramembranous ossification at the bone surface

• only in mature bones

what is the process of appositional growth

osteoblasts in the inner layer deposit osteoid tissue on the bone surface, calcify it, and become trapped in the osteocytes

circumferential lamellae

surface layers of bone

as bone diameter increases, _____ _____ widens. why does this happen?

marrow cavity

• osteoclasts dissolve tissue on the inner bone surface

flat bones develop by ____ ossification, where as long bones develop what?

• intramembranous ossification

• intramembranous, endochondral ossification, appositional

Wolff’s law of bone

architecture of a bone in determined by the mechanical stresses placed upon it

Where does the calcium and phosphate used to mineralize bone come from?

osteoblasts

resorption

dissolving bone and releasing minerals

explain the relationship between osteoclasts and osteoblasts in bone remodeling.

if the bone is used a little, osteoclasts function to get rid of extra mass. if the bone is heavily used, osteoblasts deposits new osseous tissue and thickens it.

mineral deposition (mineralization)

crystallization process in which calcium, phosphate, and other ions are taken from the blood plasma and deposited in bone tissue, mainly as hydroxyapatite

what are the steps to mineralization

1. osteoblasts lay down collagen fibers

2. collagen fibers attact the minerals from the blood

3. hydroxyapatite forms on the fibers

4. accumulation of hydroxyapatite hardens the bone

5. more crystals attract more minerals

ectopic ossification

abnormal calcification of tissues, occurs in the lungs, brain, eyes, muscles, tendons, arteries, and other organs

calculus

calcified mass in soft organs